\(\text{if we've got vertex at }(0,-1) \text{ then}\\ y = a x^2-1\\ \text{we're told that }(3,3) \text{ is on the parabola}\\ 3 = a 3^2 - 1\\ 4 = 9a\\ a = \dfrac{4}{9}\\ y = \dfrac 4 9 x^2 - 1\)

\(\text{if we've got vertex at }(0,-1) \text{ then}\\ y = a x^2-1\\ \text{we're told that }(3,3) \text{ is on the parabola}\\ 3 = a 3^2 - 1\\ 4 = 9a\\ a = \dfrac{4}{9}\\ y = \dfrac 4 9 x^2 - 1\)